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First Organ Grown From Stem Cells Alone: Report

Researchers say their advance, with livers for mice, may one day increase availability of human transplants

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Mixing cell types was important because it mimicked the same process that happens during fetal development. The different cell types use chemical signals to talk to each other, orchestrating the process of organ formation.

"There are no other groups that [I am] aware of that have tried the method described in the paper," Takebe said through a translator.

This is something which other people have kind of overlooked in their desire to develop and grow pure cell lines, that is the mixing of stem cells plus other factors that would be required for the formation of an organ, Takebe said.

After four to six days of growth in a petri dish, the liver buds, as scientists called them, were transplanted into mice where they quickly formed new blood vessels that looked like the networks of arteries and veins in adult livers. The experimental livers continued to grow for about two months in their mouse hosts.

The vessel growth was an important advance, according to one expert.

"That is a critical step forward, being able to hook it up in the blood vessels so beautifully," said Dr. Mark Donowitz, the Leboff Professor of Medicine at Johns Hopkins University in Baltimore.

Researchers tested them at various stages of development to make sure they were forming normally. After 10 days, the livers began producing human liver proteins.

The scientists even challenged the livers with medications like the painkiller ketoprofen, a drug that humans and mice metabolize differently. The urine of mice with transplanted liver buds showed byproducts of human drug metabolism, another sign that livers maintained their human origins.

In a final experiment, scientists transplanted the new liver buds into mice with liver failure. The transplanted buds improved their survival, when compared to mice in liver failure that were subjected to sham surgeries.

Despite all these promising signs, researchers said they would continue to be on the lookout for two risks in future experiments -- cancer and transplant rejection.

In addition to developing into new kinds of organs and tissues, stem cells can also turn into tumors, a problem that's a constant worry in the field of regenerative medicine.

And because the organs were grown from cell lines taken from three different humans, they might be rejected by the immune system of the eventual host. For that reason, researchers think people who receive these kinds of lab-grown organs may still need anti-rejection drugs.